Calculation of thermodynamic
properties in the application is based on the most exact formulations of
thermodynamic properties of moist air currently available. These formulations
are approved by ASHRAE
(American Society of Heating, Refrigeration and Air-conditioning Engineers) as documented in the 1997
ASHRAE Handbook "Fundamentals". Hyland and Wexler presented the equation of
state in:

Formulations for the
thermodynamic properties of the saturated phases of H2O from 173.15 K to 473.15
K, W. Hyland and A.Wexler, ASHRAE Transactions, 89(2A) 500-519, 1983.

Formulations for the
thermodynamic properties of dry air from 173.15 K to 473.15 K, and of saturated
moist air from 173.15 K to 372.15 K, at pressures to 5 MPa, R. W. Hyland and A.
Wexler, ASHRAE Transactions, 89(2A) 520-535, 1983.

Thermodynamic properties

Range of validity

The entire set of equations
used by the HumidAirWeb - Psychrometric Calculator application for calculation of thermodynamic
properties, is defined by the following temperature and pressure range:

SI Units

173.15 K <= T < = 473.15 K

0.000001 MPa < p < = 5 MPa .

-100 °C <= T < = 200 °C

0.00001 bar < p < = 50 bar .

English Units

-148 °F <= T < = 392 °F

0.000145037 psi < p < = 725 psi .

Moist Air Properties Limits

The upper limit of the absolute pressure is set at 5 MPa, and the
temperature is restricted to the range -100 to 200°C. However, for any given
absolute pressure, the highest temperature cannot exceed that temperature at
which the saturation vapor pressure equals the absolute pressure.

In other words, moist air properties are valid for any dry-bulb temperatures below or equal to the saturation temperature of water
at the same given absolute pressure, above that limit saturated moist air cannot exist.

Reference state

IMPORTANT:

In the used formulations for calculation of thermodynamic properties of moist air, the reference state
(zero enthalpy) is set at 0 °C. On some psychrometric charts (especially in the US)
the reference state (zero enthalpy) is set at 0 °F.

As a consequence, enthalpy and entropy values calculated by the library will be
shifted on these charts for the difference between reference points.

Since for any process calculation only enthalpy difference (in and out of a process)
is important, the reference point doesn't really matter.

If you want to reproduce enthalpy values from such charts, you should find the enthalpy
difference for one point (doesn't matter which one), and then add that value for all
calculated enthalpies. The same applies for entropy values.

Input variables

To calculate properties,
Psychrometric Calculator allows up to 21 different combinations of input variables in SI or English units:

The CSV Unicode format will save properly some special characters contained in
the definition of units. Since CSV is just a text file you can open a saved file
with any text editor, for example Notepad.

Select Units

In the "Units"
group box, on the "Setup Pane", set units as required, SI and English units are available.

Calculate properties

Calculation procedure

In order to calculate properties of the moist air use the following steps:

Choose units, SI or English;

Select one of the 21 different functions based on available input variables;

Enter data for the first parameter;

Enter data for the second parameter;

Enter data for the third parameter;

Press the Calculate button to perform calculation.

Detailed result
of a calculation is displayed in the main table, located in the lower part
of the input form, and also 14 main properties are displayed in the
Output Pane. Input arguments used for calculation are displayed in red.

In the Output Pane results are always inserted at the top, so you don't have to
scroll to see the latest result.

To calculate sensible heat flow, latent heat flow,
total heat flow and sensible heat factor, use the following steps:

Select "Heating / Cooling" tab;

In the "Inlet Point" group box enter parameters of the first point;

In the "Outlet Point" group box enter parameters of the second point;

Press the "Calculate" button.

The solver can handle all of the following heating and cooling processes:

Humidifying only;

Heating and humidifying;

Sensible heating only;

Chemical dehumidifying;

Dehumidifying only;

Cooling and dehumidifying;

Sensible cooling only;

Evaporative cooling.

Results of the calculation will be displayed in the first empty "results" column
in the main pane. Depending on the input parameters heating or cooling flows will be calculated.

Before making the fourth calculation, press the "Clear results" button to clear
results from the 3 available result columns in the main pane.

For each calculation, calculated inlet and outlet conditions will be displayed in the Output Pane as well. To
distinguish heating / cooling results from other data, for heating process rows will be displayed in red and for cooling process in blue.

The last two columns in the Output Pane (Process and Point) provide a description of a calculated point.

In the Output Pane results are always inserted at the top, so you don't have to
scroll to see the latest result.

Mixing calculations

To calculate properties of a mixing process, use the following steps:

Select "Mixing" tab;

In the "Inlet Point 1" group box enter parameters of the first point;

In the "Inlet Point 2" group box enter parameters of the second point;

Press the "Calculate" button.

The solver can handle mixing points in the following areas:

Super heat (non fog) area, this is the standard case;

Super saturation (fog) are, it also calculates created moisture as fog or dropelts.

Results of the calculation will be displayed in the first empty "results" column
in the main pane. Depending on the input parameters heating or cooling flows will be calculated.

Before making the fourth calculation, press the "Clear results" button to clear
results from the 3 available result columns in the main pane.

For each calculation, calculated inlet and outlet conditions will be displayed in the Output Pane as well. To
distinguish mixing results from other data, rows with calculated values will be displayed green.

The last two columns in the Output Pane (Process and Point) provide a description of a calculated point.

In the Output Pane results are always inserted at the top, so you don't have to
scroll to see the latest result.